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· "Nitro"
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Why is it that its difficult to keep rhombeus' together (let alone trying to breed them) I have heard that they release a hormone into the water, is this true? I just don't understand why they would breed in the wild but can't even be kept together in a large tank.

also has anything besides natteri been breed in captivity?
 

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nitrofish Posted on Apr 13 2003, 08:27 AM
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Why is it that its difficult to keep rhombeus' together (let alone trying to breed them) I have heard that they release a hormone into the water, is this true? I just don't understand why they would breed in the wild but can't even be kept together in a large tank.

also has anything besides natteri been breed in captivity?
As for the hormone it is generally considered to be so. The reason they breed in the wild than in your home tank is a question of space. They have been bred in captivity but in huge public aquarios (over 1,000 gal.)

The species presently known to be to have been bred in home aquarios is:

P. nattereri (all color forms, including ternetzi).
S. spilopleura both CF and common.
P. cariba
I know of no others than those above.
 

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Have there been any studies on hormone induced or attempted hormone induced spawning in rhoms or any other piranhas? Just curious since I know of alot of other fish and amphibians that are hard to breed are bred with Pituitary, Testosterone,or other hormonal injections.
 

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The only thing close to what you are discussing is P. piraya. I have the study and how it is being massed produced in Rio SF, but don't know if they are using injections other than checking micro-gonads to determine sex. I believe another study was being done on S. spilopleura, again, nothing to suggest they are using hormones.
 

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Any personal thoughts on hormone induced spawning? Either direct injections or tank satuaration. I'm wondering what kind of chances it has of working,if it'd possibly work or just make a rhom meaner. If it could work how big or old do rhoms need to be to be sexually mature? I thought I had some ideas on the size issue until I seen your 30" rhom post that kind of has me rethinking a few things now.
 

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stilllearnin Posted on Apr 15 2003, 06:09 PM...I thought I had some ideas on the size issue until I seen your 30" rhom post that kind of has me rethinking a few things now.
Better go back and re-read it
. I had my fun for today. In serious answer to your questions. I have no idea. I would imagine hormones could be injected either way, but don't know if that would be sufficient because all indications are; species like S. rhombeus appear to be sexually active at fairly large sizes (approx: 10-13 inches TL, Shulte 1988).
 

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Found this in re-reading material (long since sent):

a unique structure found only in mature males of the glandulocaudine species, Corynopoma riisei, that was derived from the anterior gills of the first gill arches. These gill glands, which consisted of chambers that opened into the gill cavity, produce a colloidal secretion which we hypothesized may function as a pheromone. Since that time, analyses of other characiform taxa have revealed similar structures in mature males of a wide range of species. We are also carrying out a survey of characiform species to see which ones possess gill glands, as well as a detailed microscopical analysis of the any glands found.
 
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